Method and system for constant-frequency beat reception of radiosignals



Nov. 12, 1929. F. SCHROTER 1,735,134

METHOD AND SYSTEM FOR CONSTANT FREQUENCY BEAT RECEPTION OF RADIO SIGNALS Filed May 13, 1926 Patented Nov. 12, 1929 u NHTED STATES PATENT} OFFICE rnrrz Iscrrnornn; or BERLI'I GER AN AssIeNon'To GESELLSCHAFT reannnnn LOSE V'IELEGRAPHIE M. B. 11., or BERLIN, GERMANY, A CORPORATION OFYVGEEMANY METHOD AND SYSTEM FOR CONSTAN'PFR'EQUENCYBEAT RECEPTION RADIO- SIGNALS Application filed. May 13, 1926, Serial No. 108,909; and in Germany May 23, 1925.

This invention relates to the beat reception of wireless signals and serves particularly for the reception of. very short waves. It is a well-known fact that in short-wave work it is more difficult to maintain the beat frequency at a constant value than in long-wave work, also in the case of short waves, beat reception is very desirable on account of the amplification of feeble incoming signalsassociated therewith, and is by far, superior to modulation at thetransmitter or receiver end.

The'purpose ofthe invention is to produce a constant beat tone, independently of the variations of the received frequency, the beat to be preferably within the audible range in order to read the'signals' in a telephone receiver. a

The main feature of the invention consists in producing two intermediate beat frequenit constitutes the difference between two intermediate frequencies variable always in like sense andamount. The incoming oscillations in this scheme are merely usedfor transferring or carrying the two heterodyne frequencies. I

In practicing the invention, the two heterodyne or local frequencies differing from each other by a preferably audible frequency should be so chosen that they will not appreciably be passed by the selective coupling means for the beat frequencies to the following circuits. This is necessary, as otherwise, independently of the incoming oscillations, there would constantly be produced a beat tone. i

All other details can be seen from the accompanying drawing which illustrates by way of example one embodiment of the idea underlying the invention.

The antenna 1 is tuned to the incoming wave by. the usual: condenser By coils 2 I and 3 the aerial is coupled with two circuits a and 5, respectively, which are likewise tuned to'the incoming wave, the two different but constant frequencies being transferred to said circuits from the local heterodyne oscillators? and'8. The oscillators are preferably only in [loose coupling relationship Withcircuits- 4: and 5, and they should be so disposed with reference to one another that they will not influence each other. It is also necessary to so arrange circuits 4 and 5 that no appreciable coupling, except, of course, by way of the aerial itself, will exist betweenthe same. The twocircuits 4 and 5 are each connected with the grid; and the cathode of suitably back-coupled audion tubes; 9 and 10.

The plate circuits of these tubes are coupled through selective coupling means 11 and 12 with additional intermediate circuits-15, 16, F

the latter being preferably filter circuits. The differential,frequencies fed to the amplifier tubes17 and Bare further amplified by the-latter, and are coupled through coils 19 and 20 with a common audion input circuit 21. Inserted in the plate circuit of the audion: tube 22 isthe telephone receiver 23in which the; constant differential frequency of the heterodynes, v7 and 8 can be rendered audibleby proper selection of the frequencies.

The couplingmeans 1-1.and12 are so chosen that they will not pass the high frequencies of the local oscillators 7 and 8. This is attained by parallel connected condensers 13 and let which allow thepassa-ge of the high frequencies of the plate circuits of tubes 9 andlO, constituting practical-lyashort-circut for, these high frequencies. To prevent transfer of high-frequency currents to circuits 15 and 16 by capacitive action, there are used any convenient screening'or shielding means-of well-known type. r I If, in the example here chosen, the incoming frequency ism, and the frequenciesof the two local sources m1 and m1 +1n, it will be seen that in the plate circuit of tube 9 there arises the beat frequency WL-"Wbl, in the plate circuit of tube 10 the beatfrequency m1 ml n. The couplings 11 and 12 are so, arranged that will pass, only frequencies in the neighborhood of said beat frequencies mm1 and mm1a-, respectively. The tuning width or band (also of subsequent filter circuits) must be so chosen that, even in the presence of highestoccurring variations in the incoming frequency, there will still be obtained an adequate transfer to circuits 15, 16, or 21. Another point is that the coupling 11, 12, must be sufficiently loose so that the frequency a which arises in the two plate circuits of 9 and 10 by virtue of the coupling of 7 and 8 by way of the aerial willnot be passed. Another mode of selection is attainable by giving circuits 15, 16, a filter-like nature. The beat frequencies mml and 772/ )7Zl"-7L, respectively, transferred through couplings 19, 20, to circuit 21, and amplified by 17 and 18 then result in the plate circuit of audion tube 22 in a frequency which is perceivable in telephone receiver 23 or another similar indicator device.

As an example for the selection of frequencies for reception of a short wave of 30 meters with the present arrangement, the following figures may be cited. The incoming wave is m=10,000,000 cycles (Hertz). Suppose the frequency of oscillator 7 is ml 9,- 950,000, and that of local source 8 is m1+a= 9,951,000, then, the beat frequency transferred to 11 will on the average be equal to mm1=50,000, and the beat frequency transferred to 12 will be mm1a=e9,000. In the telephone, the note perceived will be constantly n=1000 periods being the difierence between the two beat frequencies varying the same amount and in like sense, in the presence of fluctuations in m. The couplings 11 and 12 are so arranged that they will not pass appreciably the very high frequencies m1 and m1+a with the result that in the absence of incoming waves, no tone will be heard in telephone 23. It will be furthermore noted that, if conditionsare appropriately chosen, a constant tone will, as a matter of fact, be received, although it may change in intensity, in spite of variations of m. The varying frequency at which is coming in, therefore, serves merely as a carrier for the constant heterodyne' frequencies through 11 and 12 to the other parts of the receiving apparatus.

Having described my invention, I claim: 1. In a radio receiving system, a tuned antenna having two coupling coils for receiving an incoming signal, two branch circuits cou pled thereto one for each of said coils and comprising a circuit tuned to the frequency of the incoming energy, two local oscillators one for each of said circuits, the frequency of said oscillators differing from each other by a constant amount, means controlled thereby for producing two intermediate beat frequencies difiering from each other by the same constant amount, a common oscillation. system and means comprising coupling devices acting selectively with reference to said frequencies for coupling said common oscillation system to each of said branch circuits and means in said common oscillation system comprising a translating device whereby signals may be interpreted.

2. A high frequency oscillation receiving system comprising an antenna tuned to the frequency of the signal desired to be received, two branch circuits each tuned to the said samefrequency coupled to said antenna, a separate local oscillator coupled to each of said branch circuits said oscillations being adapted to generate oscillations differing from each other by an audible frequency, means in each of said branches for combining the received signal oscillations, with the locally produced oscillations for'producing two beat notes difiering from each other by the said same audible frequency, a common combining circuit including an audion tube circuit and translating means, and a separate filtering and amplifying device for leading said beat notes into said common combining circuits from each of said branch circuits.

' 3. In a high frequency receiving system, an antenna tuned to the frequency of the signal to be received, two branch circuits each tuned to said same frequency coupled to said antenna, a separate local oscillator coupled to each of said branch circuits and adapted to generate oscillations the frequency thereof difiering from each other by an audible frequency, combining means in each of said branches for combining the received oscillations with the locally produced oscillations for producing two beat notes differing from each other by said same audible frequency, a combining circuit including an audion tube circuit and translating means and separate filtering and amplifying circuits for coupling said branch circuits to said combining circuit and means in each of said branch circuits for preventin the locally generated high frequency oscillations from passing through said coupling circuits.

FRITZ soHRoTER. 

